A packaging machine of the type in question and a method of forming a vacuum package are disclosed by EP 1564147 A1. There, a first and a second evacuable chamber (i.e. a chamber in which a vacuum can be created) are provided. A sealable vacuum bag is introduced in the packaging machine such that a package main section accommodating the packed product is disposed in the first chamber, whereas the opening of the bag is located in a smaller, second chamber. The advantage of this packaging machine is that different vacuums can be created in the two chambers so that the pressure applied to the package from outside is higher than the pressure prevailing in the interior of the package. This higher external pressure stabilizes sensitive products within the package, such as cheese or other porous products, which, if the pressure applied is too low, tend to release bubbles from the porous structures or in which the porous structures tend to burst, whereby the product in question will be damaged. A disadvantage of this conventional packaging machine is that it is comparatively complicated to operate.
Another packaging machine for packaging objects under vacuum is disclosed by DE 3411917 A1. Here, a sealing chamber is divided by the package into a lower chamber and an upper chamber. After creating first a predetermined vacuum, rapid, abrupt venting of the chamber establishes a pressure difference between the inside and the outside space of the package.